at the moment there are three very strong agencies in the micro market  - shutterstock, fotolia and IStock. A few years ago Istock was the dominant agency, they had over 80% of the market share. Being exclusive with istock meant,  having your files for sale in the dominant marketplace. And when Bruce was in charge istock was growing well.

But from what we hear shutterstock and IStock are around 300-400 Million each, Fotolia is probably half of that and growing well and then there are several other Players that together are probably also a few hundred Million Dollars. And then there is the Macro world and editorial if you are interested.

If you are Independent you can play all markets.

You can still send some content exclusive to a few agencies, including the Macro agencies.

it is more confusing to be indie and the market is changing all the time. but being Indie means that basically anything you produce can be sold somewhere. but you need time to learn what sells best where, there is no simple roadmap to follow.

most important is to have a low rejection rate, you should be able to have at least 80% accepted if you send content to a normal Micro agency that doesn't filter by style.

and you need to produce content every week and keep feeding the beast. of you sit back and watch your portfolio, nothing interesting will happen.

However, if you have very little time and see stock more as a little hobby and you just want to achieve 20-100 Dollars a month, then maybe try a few agencies and do go exclusive with the one you feel most comfortable with.

But if you want to maximise your income then being Indie and sending a mix of Indie and exclusive content to different agencies is the best way at the moment.

Dreamstime and fotolia allow exclusive images, so it is easy to test exclusive results as well. You just have to pay attention to any lock up periods for your files.